Process for production of hydrogen and sulfur from hydrogen sulfide as raw material

ABSTRACT

Sulfur and hydrogen are produced from hydrogen sulfide according to the present invention by bringing hydrogen sulfide into contact, at a temperature exceeding the boiling point of sulfur, with at least one member selected from the group consisting of the sulfides of molybdenum, tungsten and ruthenium to give rise to a gaseous mixture consisting of hydrogen sulfide, hydrogen and sulfur, cooling the produced mixture to separate therefrom the sulfur component in the condensed form and leave behind a gaseous mixture wherein the hydrogen component makes up the majority of the total weight thereof and subsequently removing hydrogen sulfide from this mixture by means of condensation or absorption.

BACKGROUND OF THE INVENTION

This invention relates to a process for producing sulfur and hydrogenfrom hydrogen sulfide by subjecting hydrogen sulfide to a decompositionreaction by use of a catalyst.

Petroleum refining processes of the type using hydrogen gas such as, forexample, a process for desulfurization of crude oil or heavy oil byhydrocracking and a process for desulfurization of various petroleumfractions by hydrocracking by-produce fairly large volumes of hydrogensulfide. There is every indication that the total volume of hydrogensulfide thus by-produced will increase year after year in consequence ofthe expected increase in the size of petroleum refining facilities andin the consumption of petroleum products. In the existing petroleumrefining processes, the by-produced hydrogen sulfide is generallyreleased from the reaction systems in the form of off-gas in conjunctionwith other inflammable gases. The off-gas is usually used as the fuelfor heating furnaces, for example. If the off-gas has a high hydrogensulfide content, the concentration of sulfur dioxide in the wastecombustion gas increases and causes environmental pollution. Thisnecessitates separation of hydrogen sulfide from the off-gas. Asconcerns the separated hydrogen sulfide, the need for converting it intosome other valuable substance has become pressing.

Several methods have heretofore been suggested for effective use of theby-produced hydrogen sulfide. Of these methods, the so-called Clausmethod or the modified Claus method is about the only one which hascommercial significance at all. This method comprises the steps ofseparating hydrogen sulfide from the off-gas, concentrating theseparated hydrogen sulfide and subsequently converting it intoelementary sulfur and water through a partial oxidation treatment, asindicated by the following reaction formulas: ##EQU1##

Although in this method, the sulfur component alone is recovered, thehydrogen component which is responsible for the majority of the costincurred in the desulfurization by hydrogenation is partially discardedfinally in the form of water, making the process highly uneconomical.

U.S. Pat. No. 2,979,384 teaches a method which comprises allowing alower sulfide of iron, nickel or cobalt to react with hydrogen sulfideto produce a higher sulfide and hydrogen gas and then subjecting theproduced higher sulfide to thermal decomposition to give rise to a lowersulfide and sulfur. This method, thus, involves two reactions inderiving hydrogen and sulfur from hydrogen sulfide.

Further, U.S. Pat. No. 2,839,381 granted to R. Lee and E. Grovediscloses a method which comprises causing hydrogen sulfide by-producedin the reduction with hydrogen of sulfide ore to be electrolyzed in anaqueous solution containing potassium iodide and sodium iodide so as toproduce hydrogen and sulfur and recycling the produced hydrogen to theprocess of sulfide ore reduction. For practical purpose, however, thismethod entails complicated steps of operation.

It is also known to the art that at elevated temperatures, hydrogensulfide is dissociated into hydrogen and sulfur as indicated by thefollowing formula:

    XH.sub.2 S ⃡ XH.sub.2 + S.sub.X

(wherein, S_(x) denotes the allotropes of gaseous sulfur such as S₂, S₆and S₈).

If the equilibrated dissociation is considered for X = 2, then theequilibrium constant, Kp, is 5.13 × 10.sup.⁻³ for 800°K (527°C) and 2.82× 10.sup.⁻³ for 773°K (500°C). From this value of the equilibriumconstant, the equilibrated hydrogen concentration at 500°C is calculatedto be 0.4%. This means that 0.4% of hydrogen is produced by heatinghydrogen sulfide to 500°C. In this case, however, the dissociation ofhydrogen sulfide by mere application of heat proceeds with extremeslowness so that, even after about 20 hours of heating, it will notreach the stage of equilibrated hydrogen concentration. Thus, it issubstantially impossible to detect any formed hydrogen in this reaction.To render this reaction commercially feasible at all, it is necessarythat the reaction velocity be notably heightened.

Molybdenum sulfide (MoS₂) and tungsten sulfide (WS₂), which are used forthe present invention are adpoted as shown below, either by themselvesor in the form of mullti-component catalysts (frequently supported onalumina or silica-alumina) having nickel sulfide or cobalt sulfidecombined therewith. For example, they are used as catalysts in thehydrocracking of various petroleum fractions by U.S. Pat.. No.3,267,021, as catalysts in the cracking by U.S. Pat. Nos. 3,340,422 and3,475,325 and as catalysts in the desulfurization of heavy oil, etc.None of them, however, has ever found utility in the decomposition ofhydrogen sulfide, by one step, into hydrogen and elementary sulfur.

An object of this invention is to provide an improved commerciallyuseful process for the production of hydrogen and sulfur by thedecomposition of hydrogen sulfide. Another object of this invention isto provide an improved commercially useful process for the continuousproduction of hydrogen and sulfur by the decomposition of hydrogensulfide.

SUMMARY OF THE INVENTION

To attain the objects described above, the process according to thepresent invention produces hydrogen and sulfur from hydrogen sulfide bythe steps of bringing hydrogen sulfide gas into contact, at atemperature exceeding the boiling point of sulfur, with at least onemember selected from the group consisting of the sulfides of molybdenum,tungsten and ruthenium to give rise to a gaseous mixture consisting ofhydrogen sulfide, hydrogen and sulfur, cooling this gaseous mixture forthereby condensing the sulfur and removing therefrom the sulfurcondensate, circulating the remaining gaseoous mixture into contact withthe aforementioned sulfide for thereby further decomposing hydrogensulfide to produce hydrogen and sulfide and consequently produce agaseous product containing hydrogen at a higher concentration andfinally isolating hydrogen from the gaseous product.

In the process of this invention described above, part of thecirculation gas is taken out of the reaction system continuously orintermittently and it is separated into hydrogen and hydrogen sulfide.The hydrogen thus separated is obtained as a final product. The hydrogensulfide which remains after the separation of hydrogen is recycled asthe starting material. The present invention also embraces the processwherein an amount of hydrogen sulfide equivalent to the hydrogen sulfideconsumed due to the said reaction is supplied to the recycled hydrogensulfide.

Other characteristics and other advantages of the present invention willbecome apparent from the description to be given herein below withreference to the accompanying drawing.

BRIEF EXPLANATION OF THE DRAWING

The drawing is a diagram illustrating one preferred embodiment of theapparatus employed for practicing the present invention.

DETAILED DESCRIPTION OF THE INVENTION

This invention, as the first step, causes hydrogen sulfide to be broughtinto contact at a temperature exceeding the boiling point of sulfur withat least one member selected from the group consisting of the sulfidesof molybdenum, tungsten and ruthenium. Contact of hydrogen sulfide withcobalt sulfide, nickel sulfide, iron sulfide, titanium sulfide, vanadiumsulfide, chromium sulfide, etc. also serves the purpose of acceleratingthe decomposition of hydrogen sulfide into sulfur and hydrogen. In otherwords, the three specific sulfides which are used for the process ofthis invention are as effective in catalytic function as the othersulfides just described. The difference is that the sulfides other thanthose prescribed by this invention are deprived of their catalyticactivity after certain lengths of service, whereas the three specificsullfides mentioned above maintain their activity perfectly intact overa long time of use and therefore permit continued use. In the process ofthis invention, when hydrogen sulfide is brought into contact with atleast one of the three prescribed sulfides at a temperature exceedingthe boiling point of sulfur, the decomposition of hydrogen sulfide isaccelerated greatly to produce, in high yields, a gaseous mixturecontaining hydrogen sulfide, sulfur and hydrogen. When this gaseousmixture is subsequently cooled to about 30°C, for example, the sulfurcomponent alone is condensed. The gaseous mixture which remains afterremoval of the condensed sulfur is recycled and again brought intocontact with the aforementioned catalyst at the elevated temperature.Consequently, the hydrogen sulfide component of this mixture undergoesthe same decomposition reaction as described above and gives rise tosulfur and hydrogen, producing the same gaseous mixture as mentionedabove. As this cycle of operation is repeated, the hydrogenconcentration in the gas is gradually increased. As the catalyst for theprocess of this invention, a substance as in a metallic form or a oxideform which can be sulfurized into one of the three prescribed sulfidesmay be packed in advance in the reaction apparatus and thereaftersulfurized in situ into the sulfide. The sulfides of tungsten andmolybdenum are generally used in the form of disulfides. To serve as thecatalyst, the sulfide may be used in its unsupported granular form or itmay be supported on a suitable carrier.

The decomposition of hydrogen sulfide is an endothermic reaction and theequilibrium constant involved therein is fairly large at hightemperatures. This means that the more the temperature at which hydrogensulfide is brought into contact with the catalyst increases, the moreadvantageous will it prove for the decomposition. From the practicalstandpoint, however, since hydrogen sulfide is a corrosive gas, itcauses the phenomenon of dry corrosion on the apparatus. This drycorrosion gains in severity in proportion as the temperature of theapparatus increases. The apparatus currently available for this processis geneally made of Pyrex glass, stainless steel or alloy such as ofInconel. Therefore, the highest practical temperature of the reactiontolerable for such apparatus is 1000°C, preferably about 800°C. On theother hand, the lower limit of the temperature must be higher than theboiling point of sulfur, because the formed sulfur is required to remainin a gaseous state. To ensure a commercially acceptable conversion inthe decomposition, therefore, the temperature is desired to be over450°C.

Continued removal of the formed sulfur from the reaction system is anindispensable requirement for the purpose of maintaining a highconversion in the decomposition occurring between hydrogen sulfide andthe catalyst held in contact therewith. This removal is easilyaccomplished by cooling the gas immediately after contact thereof withthe catalyst.

When hydrogen sulfide is brought into contact with at least one memberselected from the group consisting of the sulfides of molybdenum,tungsten and ruthenium and, at the same time, the formed sulfur isremoved as it occurs in the system, the hydrogen concentration in thecirculation gas gradually increases as the circulation of the gas isrepeated.

Then from the gaseous mixture wherein the hydrogen concentration hasincreased because of the repeated circulation, the hydrogen componentalone is removed. Since the gaseous mixture at this stage containshydrogen sulfide component alone besides the hydrogen component, thisseparation of hydrogen is accomplished by removing hydrogen sulfide fromthe mixture. The removal of hydrogen sulfide is mdade by condensation orby absorption by, for example, resorting to the amine absorption method.Hydrogen sulfide boils at -59.6°C and melts at -82.9°C and, therefore,can easily be condensed by cooling. It can otherwise be removed bypassing the gaseous mixture through an absorbent such as an aqueoussolution of organic amine, for example, diethanolamine.

The gas which remains after removal of the hydrogen sulfide componentconsists solely of hydrogen. Thus, this gas can be obtained as a finalproduct without further treatment. The hydrogen sulfide which has beenremoved in a condensed state is readily gasified. The hydrogen sulfidewhich has been removed by absorption is easily separated from theabsorbent by utilizing the effect of temperature change upon theabsorption-desorption equilibrium. Thus, the removed hydrogen sulfide isreadily recovered in a gaseous state and delivered for furtherproduction of sulfur and hydrogen.

The present invention also provides a process by which the formedhydrogen is removed continuously or intermittently from the gaseousmixture and the remaining gas consisting solely of hydrogen sulfide isbrought into contact with the catalyst to undergo the decomposition. Thefact that this process enjoys added efficiency will be explained below.

Hydrogen sulfide in its initially delivered form is now assumed to havea concentration of unity (1). It is then assumed to undergo a process inwhich it is first decomposed, the sulfur formed in consequence of thedecomposition is continuously removed from the reaction mixture and thegas remaining after the removal of sulfur is continuously circulatedback into contact with the catalyst to establish a new equilibrium. Thefollowing table shows how molar concentrations of hydrogen sulfide andhydrogen vary after successive cycles of passage through the catalystbed when the decomposition is effected at 500°C.

                  Table 1                                                         ______________________________________                                        Cycle of passage                                                                           Unaltered H.sub.2 S                                                                        Formed H.sub.2                                      through catalyst bed                                                          ______________________________________                                        0            1            0                                                   1            0.9960       4.00×10.sup..sup.-3                           2            0.9929       7.11  "                                             3            0.9910       9.03  "                                             4            0.9896       10.45  "                                            5            0.9884       11.61  "                                            6            0.9874       12.59  "                                            7            0.9866       13.44  "                                            8            0.9858       14.21  "                                            9            0.9851       14.89  "                                            ______________________________________                                    

The table clearly shows that so long as hydrogen remains unremoved inthe reaction mixture, the conversion by the passage through the catalystbed continues to decline with the increasing number of cycles. Ifhydrogen is removed in conjunction with sulfur, then the conversionought to assume the same value in every successive cycle as in the firstcycle. To obtain hydrogen advantageously, therefore, it is desirablethat the formed hydrogen be intermittently or continuously separatedfrom the reaction gas and taken out of the reaction system.

Commercially feasible continuous operation of the present invention canbe accomplished perfectly by effecting the separation of sulfur in thesame way as by the aforementioned process and carrying out theseparation of hydrogen as indicated below: Part of the gas undercirculation is taken out continuously and then separated into hydrogensulfide and hydrogen in the same way as described above to obtain theseparated hydrogen as a final product and the remaining hydrogen sulfideis supplied, in conjunction with freshly supplied hydrogen sulfide, tothe catalyst.

Now, the working of the present invention will be described in furtherdetail with reference to the accompanying drawing.

Numeral symbol 1 denotes a reactor for the decomposition. A requiredamount of catalyst 2 is packed in the form of a layer inside thereactor. A heating coil 3 is adapted to heat the reactor externally.Denoted by 4 is a preheater connected to the anterior extremity of thereactor. The preheater 4 is maintained by a heating coil 3' attemperatures in the range of from 450° to 700°C. A postheater 5 which isconnected to the posterior extremity of the reactor is adapted to beheated to the neighborhood of 180° to 250°C by a heating coil 3" so asto keep the sulfur component in the produced reaction gas from beingcondensed. The preheater 4, the reactor 1 and the post-heater 5 are madeof Pyrex glass, stainless steel or alloy such as Inconel and constitutein their combined form a system for converting hydrogen sulfide intogaseous sulfur and hydrogen.

Hydrogen sulfide as the raw material is forwarded in a suitable amountunder normal pressure or reduced pressure through a pipe 6 and a valve 7and introduced, in conjunction with the circulation gas received througha pipe 8, into the preheater 4 via a feed pipe 9. The decompositioninvolved in the process of this invention need not be performed under anincreased pressure, because the decomposition is of a type which resultsin an increase in the mol number. After a prescribed amount of hydrogensulfide has been introduced into the reaction system, the valve 7 isclosed to seal hydrogen sulfide inside the reaction system. It is thencirculated by a circulation pump 12 through the system to be passedthrough the catalyst bed 2 repeatedly. The reaction gas which hasdeparted from the reactor 1 is sent through the post-heater 5 which isheated to about 180° to 250°C to prevent the gaseous sulfur from beingcondensed on the inner wall of the reaction system. After its travelpast the post-heater, it is led via a pipe 10 into a sulfur condenser11. At the sulfur condenser 11, the sulfur component is removed to becaptured in the form of elementary sulfur from the unaltered hydrogensulfide and the formed hydrogen. As the hydrogen concentration in thereaction gas has increased to a certain extent, valves 13, 14 and 14'are so adjusted as to have the reaction gas pass a hydrogen sulfidecondenser 15, with the result that the gas is separated into hydrogensulfide and hydrogen. The hydrogen separated from hydrogen sulfide isdrawn past a vlave 16 into a hydrogen reservoir. Thereafter, a freshsupply of hydrogen sulfide is introduced through the valve 7 to make upfor shortage of hydrogen sulfide supply resulting from the reaction.Then, the aforementioned procedure is repeated on the replenishedhydrogen sulfide. The gas being circulated within the reaction system isdrawn through a valve 17 at suitable intervals to be analyzed by gaschromatography.

This reaction system enables the reaction contemplated by this inventionto be carried out continuously. To be specific, after the hydrogenconcentration in the gas under circulation has reached a prescribedlevel, hydrogen sulfide is continuously supplied at a suitable flow rateinto the reaction system through the valve 7 and, at the same time, thecirculation gas consisting preponderantly of hydrogen sulfide andhydrogen is continuously drawn out at a corresponding flow rate througha valve 16. The circulation gas thus drawn out is treated to separateand obtain hydrogen gas.

Now, the effect of the present invention will be demonstrated withworking examles to be cited herein below. It should be understood thatthe present invention is not limited to these examples. In all theexamples cited, an apparatus of the design illustrated in the attacheddrawing was employed.

EXAMPLE 1

In the reactor, 27.1 g of unsupported molybdenum sulfide (1 to 2mm indiameter) was placed and maintained at 500°C. The preheater was kept at450°C at the same time. Within the reaction system was sealed 104.7ml(s.t.p.) of hydrogen sulfide, which was circulated by the circulationpump so as to be passed through the catalyst bed repeatedly at a rate of2.6 times per minute. After 17.5 hours of this treatment, the hydrogenconcentration reached 19.5% and the amount of hydrogen present 15.9ml(s.t.p.) respectively. The elementary sulfur collected by that time inthe sulfur condenser totalled to 20mg. Since this amount of sulfurcorresponds to 14 ml (s.t.p.) of hydrogen, it is learnt that the sulfuras simple substance was recovered substantially in a stoichiometricproportion. The slight difference noted to exist between the amount ofH₂ S introduced into the reaction system and the amount of formedhydrogen and the hydrogen concentration was due to adsorption orocclusion by the catalyst of hydrogen sulfide (or hydrogen). An X-raydiffraction analysis conducted on the catalyst at the end of thereaction revealed that the catalyst had entirely the same crytallinestructure of MoS₂ as prior to the start of the reaction, indicating thatthe catalyst remained perfectly intact throughout the reaction.

COMPARATIVE EXAMPLE 1

Decomposition of hydrogen sulfide was tried by faithfully repeating theprocedure of Example 1, except for omission of the placement of acatalyst bed within the reactor. After 26 hours of the treatment, onlytraces of formed hydrogen were recognized in the system.

EXAMPLE 2

In the reaction system was sealed 122.6ml (s.t.p.) of hydrogen sulfideas the raw material, with 27.6g of unsupported molybdenum sulfide (1 to2mm in diameter) used as the carrier and the reaction temperature keptat 450°C. The reaction gas was circulated so that it passed through thecatalyst bed at a rate of 2.6 times per minute so as to effectdecomposition of hydrogen sulfide. After 21 hours of this treatment, thehydrogen concentration rose to 9.7% and the absolute amount of hydrogentotalled to 8.9ml (s.t.p.). The elementary sulfur collected within thesulfur condenser totalled to 11.5mg, a value corresponding to 8.1ml(s.t.p.) of hydrogen. The results, therefore, indicate that the hydrogensulfide in the gaseous phase was substantially stoichiometricallydecomposed to produce hydrogen and elementary sulfur.

EXAMPLE 3

In the reaction system, 132.8ml (s.t.p.) of hydrogen sulfide as rawmaterial was sealed, with 26.8g of unsupported molybdenum sulfidedeposited in position as the catalyst and the reaction temperature fixedat 550°C. The reaction gas was circulated so as to be passed through thecatalyst bed at a rate of 0.9 time per minute, with the result thathydrogen sulfide was decomposed. After 12.5 hours of this treatment, thehydrogen concentration reached 19.7% and the absolute amount of formedhydrogen 20.0ml (s.t.p.) respectively. In the sulfur condenser, theamount of elementary sulfur collected by this time was 29mg, a valuecorresponding to 20.3ml of hydrogen (s.t.p.). The results, therefore,indicate that hydrogen sulfide was stoichiometrically decomposed intohydrogen and elementary sulfur. The X-ray diffraction analysis conductedon the catalyst at the end of the reaction revealed that at the reactiontemperature of the present example, the catalyst retained substantiallythe same crystalline structure as prior to start of the reaction,indicating that the catalyst remained perfectly intact throughout thereaction.

COMPARATIVE EXAMPLE 2

Hydrogen sulfide was decomposed under entirely the same conditions as inExample 3, except for omission of the use of the catalyst in thereaction system. Even after 14 hours of the treatment, the hydrogenconcentration was barely 5%.

EXAMPLE 4

Into the reaction system was introduced 322.8ml (s.t.p.) of hydrogensulfide as the raw material, with 38.5g of unsupported molybdenumsulfide (WS ₂, 1 to 2mm in diameter) used as the catalyst and thedecomposition was carried out at a reaction temperature of 500°C. Thevelocity of reaction gas circulation was the same as in Example 1. Inthis case, about 83% of hydrogen sulfide introduced into the reactionsystem was adsorbed onto or occluded into the catalyst and about 17% ofthe hydrogen sulfide remained as a gas. The remaining hydrogen sulfidewas circulated through the catalyst bed in the reaction system. After 21hours of this circulation treatment, the hydrogen concentration reached15.0% and the absolute amount of formed hydrogen 5.8ml (s.t.p.). In thesulfur condenser, the amount of elementary sulfur collected by this timewas 8mg, a value corresponding to 5.6ml (s.t.p.) of hydrogen. Theresults, therefore, indicate that the remaining hydrogen sulfide wasstoichiometrically decomposed into hydrogen and elementary sulfur beingequal in molar ratio to each other.

EXAMPLE 5

A fixed amount of hydrogen sulfide was sealed in the reaction system,with 26.8g of unsupported molybdenum sulfide (MoS₂, 1 to 2mm indiameter) used as the catalyst and the reaction temperature kept at550°C. The reaction gas was circulated to pass through the catalyst bedat a rate of 0.9 time per minute to effect decomposition of hydrogensulfide. At the end of 4 hours of this treatment, the reaction gas wasseparated into hydrogen sulfide and hydrogen in the hydrogen sulfidecondenser. The hydrogen thus separated was transferred into thereservoir and removed from the reaction system. The remaining hydrogensulfide was combined with freshly supplied hydrogen sulfide andsubstantially the same amount of the resultant hydrogen sulfide as usedin the initial delivery was sealed in the reaction system. Then,decomposition of hydrogen sulfide was carried out by following theprocedure faithfully. The same operation was carried out in a total offive cycles. The results were as shown in Table 2. The results show that46.2% of all the hydrogen sulfide introduced into the reaction systemwas converted into hydrogen.

                                      Table 2                                     __________________________________________________________________________    Cycle           1     2     3     4     5                                     __________________________________________________________________________    Amount of H.sub.2 S introduced                                                  (ml)(s.t.p.)  107.7 --    --    --    --                                    Added H.sub.2 S (ml)(s.t.p.)                                                                  --    19.0  8.9   15.8  17.0                                  Accumulated H.sub.2 S                                                           (ml)(s.t.p.)  107.7 126.7 135.6 151.4 168.4                                 Reaction time   4     4     4     4     4                                     Hydrogen concentration(%)                                                                     14.0  12.4  15.1  15.2  15.1                                  Amount of hydrogen (ml)                                                         (s.t.p.)      15.0  14.0  16.2  16.3  16.3                                  Accumulated H.sub.2 (ml) (s.t.p.)                                                             15.0  29.0  45.2  61.5  77.8                                  Conversion to H.sub.2 based on                                                accumulated     13.9  22.9  33.3  40.6  46.2                                  H.sub.2 S (%)                                                                 __________________________________________________________________________

In Example 3, the conversion to hydrogen based on the hydrogen sulfideas the raw material was 15.1% when the reaction was continued for 12.5hours without involving separation of hydrogen and hydrogen sulfide. Inthe present example, separation of hydrogen sulfide and hydrogen andremoval of hydrogen from the reaction system were carried out atrespectively fixed intervals. Within substantially the same time (by thethird cycle), the conversion to hydrogen based on hydrogen sulfide asthe raw material was 33.3%.

After a total of five cycles of reaction, the elementary sulfurcollected within the sulfur condenser amounted to 111mg a valuecorresponding to 77.7ml (s.t.p.) of hydrogen. The results, therefore,indicate that hydrogen sulfide was decomposed stoichiometrically intohydrogen and elementary sulfur.

EXAMPLE 6

A stated amount of hydrogen sulfide was sealed in the reaction system,with 19.7g of unsupported molybdenum sulfide (MoS₂, 1 to 2mm indiameter) deposited in position as the catalyst and the reactiontemperature fixed at 800°C. The reaction gas was circulated so as to bepassed through the catalyst bed at a rate of 0.9 time per minute toeffect decomposition of hydrogen sulfide. For the first time, a part ofthe reaction gas was separated in the hydrogen sulfide condenser intohydrogen sulfide and hydrogen by the end of 3.5 hours of reaction. Thesame separation was carried out for the second and the third timerespectively at intervals of 2 hours thereafter. Each time, theseparated hydrogen was transferred into the reservoir and removed fromthe reaction system. The remaining hydrogen sulfide was combined with afresh supply of hydrogen sulfide and substantially the same amount ofhydrogen sulfide was sealed in the reaction system and subjected toentirely the same procedure as in the first time to effect decompositionof hydrogen sulfide. A total of three cycles of operation were carriedout. The results were as shown in Table 3. The results indicate that80.4% of the entire hydrogen sulfide introduced into the reaction systemwas converted into hydrogen.

                                      Table 3                                     __________________________________________________________________________    Cycle                1    2     3                                             __________________________________________________________________________    Amount of H.sub.2 S introduced (ml) (s.t.p.)                                                       98.2 --    --                                            Added H.sub.2 S (ml) (s.t.p.)                                                                      --   55.9  62.4                                          Accumulated H.sub.2 S (ml) (s.t.p.)                                                                98.2 154.1 216.5                                         Reaction time        3.5  2.0   2.0                                           Hydrogen concentration (%)                                                                         71.1 59.9  58.2                                          Amount of hydrogen (ml) (s.t.p.)                                                                   71.5 61.3  69.6                                          Amount of H.sub.2 separated and removed                                                            56.2 48.2  --                                            (ml) (s.t.p.)                                                                 Accumulated H.sub.2 (ml) (s.t.p.)                                                                  71.5 117.5 174.0                                         Conversion to H.sub.2 based on accumulated                                                         72.8 76.2  80.4                                          H.sub.2 S (%)                                                                 __________________________________________________________________________

When the same reaction was continued for 7.5 hours without separatingand removing hydrogen, under entirely the same conditions as in thefirst cycle of operation shown in Table 3 except for the length ofreaction time, the hydrogen concentration reached 80.0% and the amountof formed hydrogen 78.6 ml (s.t.p.) respectively. Compared with theresults obtained in the case in which the separation and removal offormed hydrogen and the replenishment of hydrogen sulfide with a newsupply performed for two more cycles, the conversion to hydrogen basedon the whole amount of hydrogen sulfide supplied to the reaction systemwas practically the same while the whole amount of hydrogen sulfidetreated and the whole amount of hydrogen obtained were greater by 2.2times.

EXAMPLE 7

At 500°C, 3.0g of ruthenium supported on barium sulfate (supportedamount 5% by weight) was thoroughly pre-sulfurized with a current ofhydrogen sulfide. Then, hydrogen sulfide was decomposed by use of acirculation type reaction system. The amount of hydrogen sulfide sealedin the reaction system was 105.0 ml(s.t.p.) and the velocity of reactiongas circulation was the same as in Example 1. At the end of 20 hours ofthis treatment, the hydrogen concentration reached 16.3% and theabsolute amount of formed hydrogen 13.3 ml (s.t.p.) respectively. Theamount of elementary sulfur collected by this time within the sulfurcondenser was 18.0mg, a value corresponding to 12.6 ml (s.t.p.) ofhydrogen. The results, therefore, indicate that hydrogen sulfide wasstoichiometrically decomposed into hydrogen and elementary sulfur.

What is claimed is:
 1. In a process for the production of hydrogen andsulfur from hydrogen sulfide, the improvement which comprises:1.bringing hydrogen sulfide into contact with at least one member selectedfrom the group consisting of the sulfides of molybdenum, and rutheniumat a temperature of from 450°-800°C thereby giving rise to a gaseousmixture consisting of hydrogen sulfide, hydrogen and sulfur,
 2. coolingthe said gaseous mixture thereby condensing the sulfur component of thesaid mixture and separating and obtaining elementary sulfur, 3.circulating back to the step (1) above the gaseous mixture remainingafter removal of sulfur,
 4. subjecting the circulated gaseous mixture tothe steps (2) and (3) above continuously and recurrently for therebyforming a gaseous mixture having an increased hydrogen content and 5.separating the hydrogen component from the gaseous mixture having anincreased hydrogen content.
 2. The process of claim 1, wherein theseparation of hydrogen is accomplished by cooling the circulating gas tocondense hydrogen sulfide and removing the condensed hydrogen sulfidefrom the gas consequently to leave behind hydrogen alone in the gaseousstate.
 3. The process of claim 1, wherein the separation of hydrogen isaccomplished by passing the circulating gas through a solution capableof absorbing hydrogen sulfide alone for thereby having the hydrogensulfide component alone absorbed in the said absorbent solution andallowing the hydrogen component alone to be obtained in the gaseousstate.
 4. In a process for the continuous production of hydrogen andsulfur from hydrogen sulfide, the improvement which comprises:1.continuously bringing hydrogen sulfide into contact with at least onemember selected from the group consisting of the sulfides of molybdenum,and ruthenium at a temperature of from 450°-800°C for thereby givingrise to a gaseous mixture consisting of hydrogen sulfide, hydrogen andsulfur;
 2. continuously cooling the said gaseous mixture therebycontinuously condensing the sulfur component of the said mixture andcontinuously separating and obtaining elementary sulfur,
 3. continuouslywithdrawing a part of the gaseous mixture remaining after removal of thecondensed sulfur and, at the same time, circulating the remaining partof the gaseous mixture back to the step (1) above;
 4. separating andobtaining hydrogen from the withdrawn part of the gaseous mixture and 5.circulating back to the step (1) above the hydrogen sulfide resultingfrom the said separation of hydrogen and introducing into the said step(1) such amount of fresh hydrogen sulfide as to make up for the hydrogensulfide lost from the circulation gas in consequence of the reaction. 5.The process of claim 4, wherein the separation of hydrogen isaccomplished by cooling the withdrawn gaseous mixture for therebycondensing the hydrogen sulfide component thereof and enabling thehydrogen component alone to be obtained in the gaseous state.
 6. Theprocess of claim 4, wherein the separation of hydrogen is accomplishedby passing the withdrawn gaseous mixture through a solution capable ofabsorbing hydrogen sulfide alone thereby having the hydrogen sulfidecomponent alone absorbed in the said absorbent solution and allowing thehydrogen component alone to be obtained in the gaseous state.